1. Field
The present invention relates to a fuel cell, and more particularly to a fuel cell with an improved seal member.
2. Description of the Related Art
A fuel cell, for example, a direct methanol fuel cell (DMFC) of the active type has a structure provided with a single cell comprising: a membrane assembly electrode unit including a fuel electrode to which an aqueous methanol solution is supplied as a fuel, an air electrode to which an oxidizing gas is supplied, and an electrolyte membrane interposed between the electrodes; a fuel separator and an oxidizing gas separator disposed at both sides of the membrane assembly electrode unit; and seal members respectively disposed between the membrane assembly electrode unit and the fuel separator and between the membrane assembly electrode unit and the oxidizing gas separator.
The seal member to be assembled in the single cell is required to have the following properties in order to fulfill its functions.
(1) High resistance to the aqueous methanol solution supplied to the fuel electrode.
(2) Excellent impermeability to the oxidizing gas (for example, air) supplied to the air electrode.
(3) High resistance to radical seeds generated by an electrode reaction or radical seeds generated by an electric field in a battery.
Jpn. Pat. Appln. KOKAI Publication No. 2004-39341 discloses that the seal member (gasket) is composed of a rubber material such as silicone rubber.
Such a seal member made of rubber has an excellent impermeability to the oxidizing gas mentioned in (2). However, the seal member expands, shrinks and deteriorates in the presence of the aqueous methanol solution. The seal member also deteriorates due to the effects of radical seeds generated by the electrode reaction or radical seeds generated by the electric field in the battery. As a result, the original elasticity of rubber for composing the seal member is lowered, and the sealing performance of the membrane assembly electrode unit and passage plates is lowered. A decline in the sealing performance leads to leakage of a fuel and oxidizing gas, or disintegration of the stack structure of the single cell, thereby lowering the output or lowering the long-range reliability of the fuel cell.